The interaction of dietary carotenoids with radical species

Dietary carotenoids react with a wide range of radicals such as CCl3O2., RS O2., NO2., and various arylperoxyl radicals via electron transfer producing the radical cation of the carotenoid. Less strongly oxidizing radicals, su ch as alkylperoxyl radicals, can lead to hydrogen atom transfer generating the neutral carotene radical. Other processes can also arise such as adduct formation with sulphur-centered radicals. The oxidation potentials have be en established, showing that, in Triton X-100 micelles, lycopene is the eas iest carotenoid to oxidize to its radical cation and astaxanthin is the mos t difficult. The interaction of carotenoids and carotenoid radicals with ot her antioxidants is of importance with respect to anti- and possibly pro-ox idative reactions of carotenoids. In polar environments the vitamin E (alph a -tocopherol) radical cation is deprotonated (TOH.+ --> TO. + H+) and TO. does not react with carotenoids, whereas in nonpolar environments such as h exane, TOH.+ is converted to TOH by hydrocarbon carotenoids, However, the n ature of the reaction between the tocopherol and various carotenoids shows a marked variation depending on the specific tocopherol homologue, The radi cal cations of the carotenoids all react with vitamin C so as to "repair" t he carotenoid, (C) 2001 Academic Press.